The present invention relates to a coupler device and, more particularly, to a coupler device having driver circuits serving as transmitters and receivers which can convert digital electrical signals to optical signals and optical signals to digital electrical signals, respectively, so as to provide for optical communications between first and second digital equipment.
Communication networks that employ optical fibers are the technology of choice because they are capable of transmitting billions of bits of information per second and, unlike communication networks employing electrical cables that transfer electrical pulses, the optical fibers transmit light pulses representative of these bits that are not affected by random radiation in the environment. Further, the optical fibers are lightweight and relatively inexpensive as compared to coaxial and copper cables used in previous communication networks.
The coaxial and copper cables that interconnect electronic gear forming communication networks are relatively heavy which not only hinder their initial installation but also remain an operating drawback. For example, on a modern warship fully equipped with computers and other electronic gear which forms a communication network, the coaxial and copper cables alone can weigh up to 80 tons which may correspond to about one percent of the ship's total weight. The replacement of these coaxial and copper cables with fiber optical cables not only reduces the attendant weight, but also improves the transmission characteristics of the related communication network so that it is free from electromagnetic interference (EMI) and radio frequency interference (RFI) drawbacks.
Although optical communications between digital equipment such as computers, is desired, existing interfaces do not lend themselves to such a communication technique. More particularly, communication networks that include computers found in military installations employ a NTDS protocol which comprises a parallel transmission technique conforming to military specification, such as Military Standard, Input/Output Interfaces, Standard Digital Data, Navy System, MIL-STD-1397B (NAVY), herein incorporated by reference and which describes the parameters of digital data interfaces, such as the Navy Tactical Data System (NTDS) which is of particular importance to the present invention.
The NTDS interfaces have a specified protocol that includes not only parallel transmission techniques, but also a set of hardware logic levels for each bit of data that is transferred between digital equipment. Conversely, the optical communications commonly employ serial transmissions technique. The serial transmission technique allows all related data to be conveyed on one fiber optic, whereas the parallel transmission technique requires a separate conveyance path for each line of the parallel group of data. If a parallel transmission technique was used in an optical communication network, it would disadvantageously increase the cost by requiring separate fiber optics for each parallel bit. Further, the hardware protocol that accompanies the optical transmission commonly comprises emitter coupled logic (ECL), whereas the hardware that accompanies the NTDS protocol disadvantageously comprises logic levels that are different from the emitter coupled logic. Accordingly, although the optical communication network may be the technology of choice for military as well as commercial applications, the existing military technology, in particular, the NTDS protocol used in military applications hinders its acceptance. It is desired that means be provided to allow for the military digital equipment employing NTDS protocol to be adapted to provide for optical communication between the various digital equipment.